1. Field of the Invention
The invention relates to biomarkers for diagnosing renal diseases or for predicting the risk of a patient for developing a renal disease. More specifically, the invention provides ubiquitin fragment having a m/z of 6188, ubiquitin ribosomal fusion protein UbA52, and beta-2-microglobulin for methods of diagnosing or predicting renal diseases.
2. Background of the Invention
The number of patients with end stage renal disease is increasing at an enormous rate worldwide. This is mainly due to the rapidly increasing number of patients with diabetic nephropathy. Diabetes is, after arterial hypertension, the second most common disease in industrialized countries. According to the ADA (“American Diabetes Association”)-criteria, the incidence is estimated to be around 8.5-9 percent. Incidence and prevalence, particularly of type 2 diabetes, have increased with an unproportional increase in prevalence. This is mainly due to reduced cardiovascular mortality in type 2 diabetics. Thus, a higher percentage of diabetics live long enough to develop other complications of the disease, including retinopathy and nephropathy. Whereas the incidence of nephropathy in type-1 diabetics is between 20 und 40 percent after a disease duration of 15-30 years, 10-50 percent of type 2-diabetics will develop renal involvement. Diabetic patients with renal disease have a poor prognosis. Compared to non-diabetics on dialysis, diabetics have a 22 percent increased first-year mortality and a 15 percent elevated 5-year mortality. Estimated costs for a diabetic dialysis patient are approximately 51,000 US $ per year compared to 39,000 US $ for non-diabetics. Risk factors for the development of diabetic nephropathy include genetic predisposition, poor glycemic control, arterial hypertension, and smoking.
At present, the definite diagnosis of nephropathy, such as diabetic nephropathy, is based on findings in renal biopsy. However, in most cases, the diagnosis can be reliably made in patients with macroalbuminuria in the presence of diabetic retinopathy. Microalbuminuria occurs when the kidney leaks small amounts of albumin into the urine. In a properly functioning body, albumin is not normally present in urine, because it is filtered from the bloodstream by the kidneys. In type 1 diabetics, microalbuminuria is the best predictor of subsequent development of nephropathy (defined as persistent macroalbuminuria (>300 mg/24 h)), with approximately 50 per cent of patients with microalbuminaria progressing to overt nephropathy. Conversely, microalbuminuria is of lesser value in type 2 diabetics, since these patients are older, with microalbuminuria often being induced by a variety of causes, including arterial hypertension or heart failure (Mykkanen L, et al., 1994). Thus, the predictive value of microalbuminuria is less strict.
Concerning diabetic nephropathy, proteomics have recently been applied with success to analyse kidney tissues from rodent models (Thongboonkerd V, et al (2004); Thongboonkerd V, et al. (2005)), but the larger amounts of material needed is a limiting factor for applications in human biopsies (Susztak K, et al. (2006)). The non-invasive and easy sampling of urine makes it attractive for proteomic analyses. Urinary proteomics were already applied to study type 2 diabetes and diabetic nephropathy (Hong C Y, et al. (2003); Rossing K, et al. (2005)).
Thus, in order to identify patients at risk for developing renal disease such as diabetic nephropathy, and in order to reliably diagnose renal diseases, additional markers are urgently needed.
Muller G A et al. (2007) generally describe the use of various techniques for proteomic analysis that can be used for monitoring renal disease-related protein changes, which may be useful for diagnostic tests.
Dihazi et al., Nephrology (2005a), describe the identification of biomarkers indicative of nephropathy in urine by way of mass spectrometry. The report mentions the m/z ratios of various prospective proteins found, but only identifies one of these proteins further.
Sun L et al., JBC (2002) describe the up-regulation of the mouse UbA52 gene in kidney tissue of newborn diabetic mice. The report speculates that UbA52 might be relevant to the pathobiology of diabetic nephropathy. In the kidney, the UbA52 was exclusively located in renal tubules, and its expression in mice kidney was found to be proportional to the glucose levels in blood. Gene expression analyses displayed an over-expression of the UbA52 protein in kidney of diabetic newborn mice.
Further, Schardijn and Statius showed a strong correlation between the β2-M level in serum and the glomerular filtration rate (Schardijn G, et al. (1979); Schardijn G H, et al., (1987)). Alteration in β2-M level has been observed in patients with different diseases, including diabetic nephropathy (Schaub S, et al. (2005); ); Schardijn G H, et al., (1987); Hong C Y, et al. (1998)).